This invention relates to a communication apparatus which is operable as a node station in a communication network system and which is communicable with the other node stations.
As a communication network system of the type described, known is a local area network system comprising a plurality of node stations which are connected to one another like a loop to transmit or receive a sequence of data signals to or from the other node stations. Each of the node stations may be referred to as a communication apparatus communicable with the others through the loop. The data signal sequence is divided into a succession of data frames. In this event, an address is assigned to each of the communication apparatus to individually specify the communication apparatus.
In the communication network system, it often happens that an identical data signal is delivered to a plurality of the communication apparatus through the loop and is sent to the respective communication apparatus by the use of a broadcast frame. The broadcast frame is distinguished from the remaining data frames by the use of a specific information signal which is indicative of the broadcast frame and which is located at a predetermined time slot in the broadcast frame.
In the meanwhile, it is a recent trend that a wide variety of information signals are transmitted by the use of the broadcast frame to be given to a plurality of the communication apparatus in parallel. This shows that various kinds of the broadcast frames are transmitted on the loop and received by the plurality of the communication apparatus.
However, all of the broadcast frames may not be always delivered to and received by all of the communication apparatus connected to the loop. Under the circumstances, the communication apparatus should individually judge whether or not reception broadcast frames include data signals necessary for the respective communication apparatus and should discard the data signals, if they are unnecessary for the communication apparatus.
To this end, each of the node stations or communication apparatus is provided with an information processing device composed of a main processor.
Herein, it is to be noted that such a main processor should process a great number of jobs in connection with communication carried out among the communication apparatus on the loop. Therefore, when judgement of such a broadcast frame is made in the main processor in addition to the above-mentioned jobs, a heavy load is excessively imposed on the main processor. This results in a reduction of throughput of the main processor.